Blocking impulse generator



Nov. 12, 1946.

o. H. SCHADE BLOCKING IMPULSE GENERATOR Filed June 24, 1942 v v Bnnehtor H. cnADE 6M Ono (Ittomeg Patented Nov. 12, 1946 IBLOCKING'VIMPULSE GENERATOR m H. Schade, West Caldwell, N. J., assignor to 1 Radio Corporation of America, a corporationof Delaware ApplicationJune 24, 1942, Serial Nb. 448,210

This invention relates to circuits for producing-electrical impulses, and particularly to blocking impulse generators. A blocking impulse generatoris a circuit which is normally quiescent, he, the voltages atvarious points in-the circuit remain constant, until a trigger or control impulse is applied, whereupon the circuit voltages vary through an operating cycle and then resume their former values. Such circuits usually comprise an oscillator of some sort, biased to prevent oscillation. The blocking bias is momentarily overcome by the trigger impulse, the oscillator goes through one cycle, and is blocked again. The duration, wave shape and amplitude of the output pulse are determined by the constants of the oscillator circuit while the trigger pulse determines only the time at which an output pulse is initiated. Circuits of the described type find application, for example, in deflection circuits for cathodeiray tubes. A i

It an object of the invention to provide an improved method of and means for producing pulses ofpredetermined duration, amplitude, and wave} shape at a repetition rate determined by the frequency of a controlling pulse.

A further object is to provide an improved method of and means for producing pulses having duration, amplitude and wave shape independent of their repetition time and. independent oithe wave shape of the pulse used to control their repetition time.

Another object of the invention is to provide an improved method of and means for maintaining constant pulse shape and duration without circuit adjustments over a wide range of pulse frequency.

Still another object is to provide a method of andmeans for producing pulses of predetermined duration and wave shape having a predetermined time delay with respect to their respective control impulses, independent of the repetition rate.

Other and incidental objects will become apparent to those skilled in the art upon consideration of the following description with reference to the'accompanying drawing, of which Fig. 1 is a circuit diagram of a transformer coupled blocked oscillator type impulse generator, Fig. 2 is a circuit diagram of a blocked multivibrator 4 Claims. (Cl. 250-36) type'impulse generator and Fig. 3 is a schematic diagram of a pulse delay circuit. Figs. 4, 5 and 6 are graphical representations of the wave forms of voltages appearing at various points in the circuits during the operation of the devices shown in Figs. 1, 2 and 3 respectively.

Referring to Fig. 1, a vacuum tube I, is connected to the coupled primary windings 3 and 5 of a transformer ,I. so asto feed back energy from the plate circuit to the grid in such polarity as to tend to produce oscillation at a frequency determined by the circuit constants. A resistor I I is connected in the cathode circuit of the tube I, and a resistor 9 is connected from the positive plate Voltage supply terminal to the resistor II. Current flowing from the plate supply (not shown) through the resistors 9 and II produces a voltage drop in'the resistor II sufficient to out off the tube I and prevent oscillation.

A resistor I3 is connected in the grid A.-C. return circuit in series with the transformer winding 5, so that a positive voltage impulse I9 applied across resistor I3 will overcome the grid biasing effect of the voltage drop on the resistor II. Control impulses I9 may be applied to the circuit at a terminal I5, which is connected through a capacitor IT to the resistor I3. The value of the capacitor I1 is selected with reference to that of the resistor I3 so that a pulse I9 applied at the terminal I5 will be differentiated to provide a sharply defined pulse ZI at the beginning of each control pulse I9.

The circuit will oscillate for one-half cycleas each pulse ZI reaches the grid circuit, producing an output pulse 23 at the secondary 25 of the transformer I. At the end of the half cycle, the voltage fed back from the plate circuit to the grid circuit cuts off the tube I because of the charge on capacitor I8 and the tube remains cut off by the voltage across the resistor II until another pulse 2| arrives at the grid circuit. Thus, the repetition frequency of the output pulse is determined solely, by that of the control pulse I9, while the wave shape, duration, and amplitude of the output pulse depend on the oscillator circuit and are independent of frequency.

Referring to Fig. 4, the curve a. represents the voltage across the resistor I3 as a functionof time, the curve 2) represents the total voltage between the grid and the cathode of the tube i, and the dotted linec represents the voltage across the resistor II. I

Referring to Fig. 2, a blocking impulse generator including a multivibrator circuit is illustrated. 'I'he multivibrator circuit is of the type described inU. S. Patent No. 2,157,434 to J.L. Potter, and comprises tubes 29 and 3| provided with a common cathode resistor 33 and plate load resistors 35 and 31. The plate of the first tube 29 is coupled through a capacitor II to the grid of the second tube 3|, which is connected to ground through a grid leak 43. The various circuit constants are so proportioned that cyclically repeating voltage pulses would be produced across the resistors 33 and 31, if the circuit were allowed to operate as described in the said Potter patent.

This type of operation is prevented by a resistor 21 connected between the positive terminal of the plate voltage supply and the common cathode circuit. Current from theplate flows through the resistors 21' and 33, producing sufficient voltage drop on the resistor 33 to cut off the second tube 3|. A resistor 44 is coupled to the grid of the first tube 29 througha capacitor 45 so that a negative voltage impulse 49 applied across the resistor 44 througha capacitor 41 will reach the grid of the tube 29 in the proper polarity to reduce the positive grid bias of tube 29 momentarily causing an amplified positive im'- pulse on the grid of the tube 3|, which in turn causes the circuit to produce, by current feedback in resistor 33, one pulse in the plate circuit of the tube 3I. The duration of the pulse 5| is controlled predominantly by. the product of the resistor 35 and the capacitor 4|, and is independent of the repetition time, which is controlled by the input pulse 49. The time constant represented by the product of the resistor 43 and the capacitor 4| must be less than one-third of the minimum pulse repetition time in order to assure discharge of the capacitor 4Ibefore occurrence of the triggerv pulse. A pulse 53 similar to the pulse 5| but ofopposite polarity appears simultaneously across the resistor 33.

Referring to Fig. 5, the curve it represents the voltage across the resistor 43,. and the curve I) represents the resultant voltage at the grid of the tube 3|, for a fairly high repetition rate. For lower repetition rates the; pulse decay occupies a smaller, percentage of the totaltime per cycle.

A circuit for producing a pulse of predetermined wave shape and amplitude a predetermined time after the occurrence of a controlling pulse is shown in Fig. 3. Two blocked multivibrators 55 and 51, each like ,thefdevice shown. in Fig; 2, areemployed. The elements of the devices 55 and 51 are. designated by the same reference numerals as the corresponding elements of the circuit of Fig. 2, with prefixes I and .2 respectively.

The output of the. multivibrator 55 across a resistor I33 15' coupled through a capacitor 241 to a resistor 243 in the control input circuit of the multivibrator 51. I

The operation of the multivibrator 55 is exactly like that of the device of vFig. 2. A control pulse I49 applied to the resistor I43 through the capacitor I4'I produces a voltage shown by the curve b of Fig. 6, which overcomes the blocking bias on the tube -I3| and produces a. voltage shown by the curve 0 of Fig. 6Yacross the resistor. I33. The pulse duration of the voltage 0 is largely determinedbythe product of the resistor I35 and the capacitor, MI. The voltage. 0 is diiierentiated by the capacitor 24l and the resistor 243, resulting ina voltage at thegrid of the tube 229. showniby the curve d of Fig. 6'. The negative pulses of the voltage d lagwthe corresponding-control pulse fronts by the pulse durationtime of the voltage c,,and produce outputpulses 25| and 253, illustrated in Fig. 6 by the curves e and 1 respectively. The delay of the output pulses over the corresponding control pulses is controlled by the time constant represented by product of the resistor I35 and the ca pacitor MI, and is independent of the repetition frequency of the pulse I49.

I claim as my invention:

1. A pulse generator comprising two oscillator devices including elements so proportioned that said devices tend to oscillate and block at a frequency higher than the repetition frequency of the highest frequency pulse to be generated; means for applying a bias to each of said devices to prevent oscillation; means for applying a pulsating controlvvoltage to one of said devices to momentarily overcome said bias on said first device' in response to each pulse of said control voltage, whereby said first device produces, in response to each pulse of the control voltage, a pulsehaving a duration time determined by the circuit elements of said first oscillator device; means for deriving a voltage proportional to the rate of change of the output voltage of said. first .for applying the output offthe first of saidoscillator devices to the second of said devices.

3. A system for producing a pulse in response to a control pulse ata predetermined time after the occurrence of said control pulse comprising two normally blocked oscillator devices; means for applying said control pulse to one of said, oscillators to cause said oscillator to produce v an output pulse of predetermined duration;- means for deriving from said output pulses. voltage proportional to the time derivative of said-output pulse and for applying said-derived voltageto the otherof said oscillator devices. r

4. A system for producing .pulsesof predeter-- minedmagnitude and Wave shape and a repetition frequencydetermined by that of a pulsating control voltage, comprising two electron :discharge tubes each including a cathode, an-anode anda control grid, a source of anode potential connected to the anodes 'of'said. tubes through load resistors andto the cathodes ofsaid'tubes through a common cathode resistor, means for coupling the anode of the first of 'said tubes to the control grid of the secondof said tubes whereby said tubes tend to oscillate at a-frequency higher than that ofith'e highest frequency pulse to be generated, a resistor connectedbetween the positive terminal of said sourceof. anode potential and said cathodes .to provide sufiieient drop in said cathode resistor to bias said secondtube to cut'o'tlfa resistor connected'be tween said positive terminal'andlthe control grid: 

